In an energy-assisted magnetic recording (EAMR) system (e.g., hard disk), the minimum written bit size in the media is controlled by the minimum optical spot size produced by a near field transducer (NFT) acting as a plasmon element. In one design, the NFT has two portions, such as a disc and a pin, that serve different purposes. The disc converts electromagnetic energy of incident light into surface plasmons, and the pin channels a highly localized surface plasmon field to an air bearing surface (ABS). The performance of the NFT, both electric field intensity and spot size, depends on a number of NFT parameters such as core-NFT spacing, NFT-spacer interface, NFT size, NFT shape, NFT thickness, pin length, pin width, pin thickness, and NFT material. Additionally, the performance depends on the illumination conditions which are determined by the waveguide geometry (e.g., solid immersion mirror or channel waveguide) and grating coupler design.
In the related art, device characterization is generally performed at bar or slider level. However, bar or slider level testing is a time consuming and expensive process because it involves many backend processes (e.g., lapping process and other processes). Therefore, it is desirable to develop better methods and apparatuses to characterize the performance of the NFT such that the testing and development cycle can be reduced.